DESCRIPTION (Adapted from the applicant's description) Encephalopathy represents a common and serious manifestation of HIV-1 infection. Approximately one third of adults and half of children with AIDS have neurologic complications which are directly attributable to infection of the central nervous system (CNS) by HIV-1. At present it is unclear how HIV-1 enters the CNS and causes encephalopathy. Several lines of evidence suggest that viral invasion into the CNS is mediated through cell-associated HIV-1 in CD4+T cells and monocytes that traffic across the blood-brain barrier. We isolated and cultivated human brain microvascular endothelial cells (HBMEC) from children and adults, which constitute the blood-brain barrier. We showed that gp 120 was able to upregulate the expression of cell adhesion molecules (VCAM-1, ICAM-1) and PECAM-1 phosphorylation in both children and adults' HBMEC. We also showed that HBMEC derived from children possess the molecules identified for receptors/co-receptors for HIV-1 and gp 120, e.g., CD4, sulfatide and B chemokine receptor, and anti-CD4 antibodies blocked gp 120-mediated activation in children's HBMEC, but not in adults' HBMEC. Moreover, gp 120-mediated responses in HBMEC were blocked by platelet-activating factor (PAF) receptor antagonists as well as inhibitors of both protein kinase C and tyrosine kinase. The overall aim of this application is to further characterize the gp 120-mediated activation of HBMEC. Specific Aims are as follows: 1. To further examine and compare characteristics of human brain microvascular endothelial cells (HBMEC) derived from children vs. Adults. 2. To further investigate and compare gp 120-mediated cell adhesion molecule expression and PECAM-1 phosphorylation in children's vs. Adults' HBMEC. 3. To assess the mechanisms by which gp 120 elicits increased cell adhesion molecule expression and PECAM-1phosphorylation in children's and adults' HBMEC, i.e., roles of CD4, sulfatide and chemokine receptors. 4. To investigate the mechanisms of gp 120 and HBMEC receptor/co-receptor interactions leading to increased cell adhesion molecule expression, PECAM-1 phosphorylation and transendothelial migration of monocytes, i.e., roles of G proteins and signaling pathways, platelet-activating factor (PAF). The information derived from this proposal should enhance our understanding of the role of HBMEC in HIV encephalopathy.